The use of ventilators and breathing circuits to assist in patient breathing is well known in the art. The ventilator and breathing circuit provides mechanical assistance to patients who are having difficulty breathing on their own. During surgery and other medical procedures, the patient is often connected to a ventilator to provide respiratory gases to the patient. One disadvantage of such breathing circuits is that the delivered air does not have a humidity level and/or temperature appropriate for the patient's lungs.
To provide air with desired humidity and/or temperature to the patient, an HME unit can be fluidly connected to the breathing circuit. As a point of reference, HME is a generic term, and can include simple condenser humidifiers, hygroscopic condenser humidifiers, hydrophobic condenser humidifiers, etc.
In general terms, HME units consist of a housing that contains a layer of heat and moisture retaining media or material (“HM media”). The HM media has the capacity to retain moisture and heat from the air that is exhaled from the patient's lungs, and then transfer the captured moisture and heat to the ventilator-provided air of the inhaled breath. The HM media can be formed of foam, paper or other suitable materials that are untreated or treated, for example, with hygroscopic material.
While the HME unit addresses the heat and humidity concerns associated with ventilator-provided air in the breathing circuit, other drawbacks may exist. For example, it is fairly common to introduce aerosolized medication particles into the breathing circuit (e.g., via a nebulizer) for delivery to the patient's lungs. However, where an HME unit is present in the breathing circuit, the medication particles will not readily traverse the HM media and thus not be delivered to the patient.
In addition, the HM media can become clogged with the droplets of liquid medication, in some instances leading to an elevated resistance of the HME unit. One approach for addressing these concerns is to remove the HME unit from the breathing circuit when introducing aerosolized medication. This step is time consuming, subject to errors and can result in the loss of recruited lung volume when the circuit is depressurized.
Alternatively, various HME units have been suggested that incorporate intricate bypass structures/valves that selectively and completely isolate the HM media from the airflow path. For example, existing bypass-type HME units employ a bypass structure that is internal or through the HM media. While viable, these and other bypass-type HME units are difficult to operate (e.g., requiring a caregiver to rotate two frictionally fitting housing units relatively to each other) and/or are relatively complex and thus expensive.
In light of the above, a need exists for improved HME units having an HM media bypass feature that addresses one or more of the problems associated with conventional bypass-type HME units.